Multiple spark gap protective device

ABSTRACT

A device providing spark gaps protection between the pins of a cathode ray tube and solid state circuitry associated therewith is disclosed. The device includes an insulated substrate, a metallic layer on the substrate and a grounding strap. The device is mounted on the base of a cathode ray tube with projections on the metallic layer extending to within a predetermined distance from the pins providing a spark gap therebetween.

United States Patent Schor et al.

[ 1 Feb. 18,1975

[ 1 MULTIPLE SPARK GAP PROTECTIVE DEVICE [75] Inventors: Ferdinand William Schor, Goleta; Tore Rudolf Johnson, Harrisburg, both of Pa.

[73] Assignee: AMP Incorporated, Harrisburg, Pa.

[22] Filed: Sept. 12, 1973 [21] Appl. No.: 396,944

[52] U.S. Cl 317/615, 313/318, 317/69,

. 339/111 [51] Int. Cl. H02h 9/06 [58] FieldofSearch ..317/6l,61.5,69;339/111, 339/194 R, 194 N;313/318 [56] References Cited UNITED STATES PATENTS 3,227,910 1/1966 Pittman 317/615 X 3,278,886 10/1966 Blumenberg et al., 339/111 X 3,502,933 3/1970 Leimontas et al. I 317/615 3,683,228 8/1972 Kleen 313/318 Primary Examiner]ames D. Trammell [57] ABSTRACT A device providing spark gaps protection between the pins of a cathode ray tube and solid state circuitry associated therewith is disclosed. The device includes an insulated substrate, a metallic layer on the substrate and a grounding strap. The device is mounted on the base ofa cathode ray tube with projections on the metallic layer extending to within a predetermined distance from the pins providing a spark gap therebetween.

1 Claim, 10 Drawing Figures PATENIED I 8195 3.867. 67 O SHEET 1 OF 2 PATENTEU FEB] 8 i975 SHEET 2 [IF 2 MULTIPLE SPARK GAP PROTECTIVE DEVICE BACKGROUND OF THE INVENTION 1. The Field Of The Invention The present invention is related to a protection device providing multiple spark gaps between the pins of a cathode ray tube and solid state circuitry associated with the control elements of the tube and in particular to a device providing for high voltage spark discharge emanating from the anode of the tube.

2. The Prior Art Many modern television receivers, especially color television receivers, are presently being manufactured with solid state circuitry replacing the previous well known vacuum tubes in order to reduce weight, cost, and service problems related to the comparatively short service life of vacuum tubes. The most commonly used solid state device is the transistor which consists of two types of semi-conducting material separated by a thin membrane of semi-conducting material, which usually acts as the controlling element. While such devices have a high degree of reliability and comparatively long life when used within their ratings, they are subject to rapid destruction when their ratings are greatly exceeded.

Large color television picture tubes are usually operated with an anode potential of 25,000 volts. The anode capacity to ground is approximately 2,000 picofarads which permits the storage of appreciable energy at this high potential. Since the energy stored is equal to 6: CE joules, the anode can store 0.625 joules or watt-seconds. If this energy were to be discharged in 10 microseconds, it would produce 62.5 kilowatts of instantaneous power. The destructive effects of such anode discharges on associated transistorized circuitry is readily apparent. Anode discharges can occur within the picture tube to any of the tube electrodes so that all semiconductor circuits associated with the picture tube must be protected.

It has become common practice to provide means of redirecting this energy so that it will not pass through the semiconductors. One method of reducing the energy passing through the semiconductors is to use a high resistance between the semiconductor and the picture-tube element. However, even a 1,000 ohm resistor will allow an initial current of 25 amperes to pass through the transistor while a resistor as large as 2,500 ohms limits the initial current to 10 amperes. Resistors of greater value would seriously impair the efficiency of the control circuit and thus are not practical.

Another method of redirecting the stored energy in the anode is to provide a low voltage spark gap to permit discharge to ground. These spark gaps usually discharge at 1,000 to 1,500 volts. The focusing grid, which operates at 6,000 volts d.c., is operated with a 10,000 volt spark gap. Thus the present practice usually provides a resistor of 1,000 to 3,000 ohms in series with the output of the semiconductor circuit connected to the picture tube elements and a spark gap to ground for each of the electrodes of the picture tube. Such a circuit is disclosed in US. Pat. No. 3,733,522.

One method of providing spark gaps for the picture tube electrodes is to incorporate a grounded metal ring within the picture tube socket closely spaced to the socket terminals. An example of this type of device may be found in US. Pat. No. 2,850,714. While this method has the advantage of simplicity of installation,

it has the disadvantage of not permitting inspection of the gaps for short circuits or excessively large gaps. Another disadvantage is that the length of the spark gap, and hence its discharge voltage, depends upon the cumulative sum of several dimensional tolerances so that the discharge voltage is subject to considerable variation. A further disadvantage is that the ground return strap must be attached to the socket in addition to all of the other control leads which forms a cumbersome assembly for handling during manufacture of the socket assembly and also during production of the complete television receiver. A still further disadvantage is that a short circuited spark gap (which would render the receiver inoperative) requires replacement of the entire socket, an expensive service operation requiring unsoldering and replacing over a dozen connecting wires.

SUMMARY OF THE INVENTION The present invention is a device having a plurality of protective spark gaps between the pins of a cathode ray tube and the associated solid state circuitry and includes an insulating substrate adapted to be mounted on the base of the picture tube, a metallic layer attached to the substrate providing an air spark gap between the layer and each of the pins of the tube, and a common ground connection to the metallic layer.

Accordingly, one of the objects of this invention is to construct a separate multiple spark gap protective device, entirely apart from a cathode ray tube socket, which can be replaced by detaching a single lead wire, namely the ground strap.

Another object of the invention is to produce a multiple spark gap protective device which can be easily inspected for short circuited spark gaps or excessively large spark gaps without disassembling any components.

yet another object of the present invention is to construct a multiple spark gap protective device which can be easily repaired.

A further object of the present invention is to produce a multiple spark gap protective device consisting of an integral unit whose dimensions can be closely controlled thus allowing close control of the length of each spark gap and hence its discharge voltage.

A still further object of the present invention is to construct a multiple spark gap protective device of simple design which can be used with presently available sockets thereby resulting in a lower overall initial cost of socket and spark gaps.

Futher features, objects and attendant advantages of the present invention will become apparent to those skilled in the art from the following detailed description taken with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded perspective view showing a first embodiment of the subject spark gap protective device together with the base of a cathode ray tube;

FIG. 2 is a vertical section through the subject spark gap protector device of FIG. I mounted on the base of a cathode ray tube;

FIG. 3 is an exploded perspective view of a second embodiment of the subject spark gap protective device;

FIG. 4 is a plan view of the embodiment of the spark gap protective device shown in FIG. 3;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. I shows a tube base fixed to the end of a typical cathode ray tube 12, only a portion of which is shown and which is the type of tube used as the picture tube in a color television receiver. Twelve pins 14 project from a like number of small truncated conical protrusions 16 extending from the free end of the base. The two pins 18 are used for the tube heater circuit and do not require spark gaps since they are nearly ground potential and are not directly associated with semiconductor circuits. The anode pin 20 is isolated from the remaining pins and operates at from 4,000 to 6,000 volts, depending upon the anode voltage and the focusing requirement. For this reason it has a much larger spark gap in order to permit breakdown at a higher voltage, usually between 8 and I2 kilovolts. The base also includes a cylindrical locating pin 22 having a radially directed key 24.

The subject spark gap protection device 26 includes two layers, one of which is an insulating substrate 28 having a keyed central aperture 30 and a plurality of holes 32 equal to the number of pins 14. The holes 32 can be cylindrical or conical, as shown in FIG. 2, and are arranged in a circle around and spaced from aperture 30. The substrate can be made from any of the well known insulating materials. A metallic layer 34 is positioned on the substrate 28 and has a somewhat similar cnfiguration inculding keyed aperture 36 and holes 38. The metal layer may be either a separate sheet of metal attachedto the substrate or may be formed directly on the substrate by any of the well known methods such as printing and etching ona sheet of plastic material, such as Mylar or Kapton. I

The device is positioned on the base 10, as shown in FIG. 2, with pins 14 and centering key 22 extending through the appropriate holes and the substrate 28 resting against the base 10. The holes 32 in the substrate serve to locate and position the device so that spark gaps 40 are formed around pins-14. A ground strap 41 is connected between the device and ground potential, such as a chassis (not shown).

The second embodiment of the subject spark gap protection device, shown in FIGS. 3 and 4, includes insulating substrate 42 and a thin metal stamping 44 containing a central aperture 46 with a series a protrusions 48 extending radially inwardly around the periphery of aperture 46. These protrusions are designed so that the spark gaps are approximately 0.012 inches in'length to provide adequate breakdown voltage. It should be noted that one of these protrusions 50 is spaced radially outwardly of the other protrusions to provide a higher voltage gap for anode pin 20 which is connected to the focusing electrode. Holes 52 are provided to accurately assemble the metal ring 44 on the insulating substrate 42. The insulating substrate 42 has a keyed center locating hole 54 corresponding to the centering key 22 of the cathode ray tube 12. A plurality of triangular shaped holes 56 in the substrate allow passage of the pins to be provided with spark gaps and also serve to align the pins to form a proper spark gap width. When the metal ring 44 is fixed on the insulating substrate 42 by rivets 60, the spark gaps 48 are properly aligned with respect to the pins for the desired breakdown voltage, as shown by the plan view in FIG. 4. Since the metal ring must be grounded, one end of a ground strap 62 is also fixed-to the metal ring. The other end of the ground strap is connected to a portion of the television receiver chassis (not shown).

The pin holes and keyed center holes in the substrate can be made out ofa plastic sheet and the pin holes can be formed with a conical depression, as in FIG. 2, if it is desired to closely fit over the cone shaped protrusions surrounding the tube pins.

The third embodiment, see FIGS. 5 and 6, is similar to the previous embodiments in that it is shown in combination with an insulating substrate 87 and a die stamped metal ring 64 and ground strap 66. The ring has a plurality of radially inwardly directed extensions 68 which are profiled to closely follow the configuration of the truncated conical projections 16 of the tube base. The length of these extensions is such that they do not touch the pins 14 but instead form a spark gap 70 with the pins. v

The fourth embodiment, see FIGS. 7 and 8, is similar to the third embodiment in that it is shown with only a die stamped metal ring 72 which has a plurality of conical portions 74 arranged to surround each protrusion 16 and form a spark gap 76 with the pins 14. A single extension 78 is formed fora spark gap with the anode pin (not shown). The ring 72 is connected to a ground strap (not shown) in the same manner as the previous embodiments.

While the fourth embodiment has been described and illustrated as having only a metal ring portion, it is clear that this same configuration could be formed with an insulated substrate and with the metal ring plated on or integrally attached to the substrate.

Another embodiment of the present invention is shown in FIGS. 9 and 10 is similar to the first embodiment. In this particular embodiment, either the metal ring 80 or the insulating substrate 82 is undercut so that the metallic ring extends in cantilever fashion to form an air spark gap 84. In this embodiment each opening 86 in the substrate 82 is such that the associated pins 14 will be properly aligned for forming a spark gap within the range tolerances.

The present invention may be subject to various modifications and changes without departing from the spirit or essential characteristics thereof. The above discussed embodiments are therefore intended to be illustrative and not restrictive of the scope of the invention.

What is claimed is:

l. A multiple apark gap protective device for protecting solid state circuitry associated with cathode ray tubes from high voltage discharges, in combination with a cathode ray tube having a plurality of pins on the base thereof and an insulating socket body containing therein a plurality of contacts connected to said circuitry and adapted to engage said pins, said device comprising:

an insulating substrate having a keyed central aperture surrounded by a circular configuration of a plurality oflesser apertures equal in number to pins on said cathode ray tube, each said lesser aperture being substantially triangular in plan view with an apex of said triangles directed radially inwardly of said substrate;

a metallic plate fixed to said substrate and having a central aperture of larger dimension than said circular configuration of lesser apertures in said substrate and a plurality of radially inwardly directed cathode ray tube. 

1. A multiple apark gap protective device for protecting solid state circuitry associated with cathode ray tubes from high voltage discharges, in combination with a cathode ray tube having a plurality of pins on the base thereof and an insulating socket body containing therein a plurality of contacts connected to said circuitry and adapted to engage said pins, said device comprising: an insulating substrate having a keyed central aperture surrounded by a circular configuration of a plurality of lesser apertures equal in number to pins on said cathode ray tube, each said lesser aperture being substantially triangular in plan view with an apex of said triangles directed radially inwardly of said substrate; a metallic plate fixed to said substrate and having a central aperture of larger dimension than said circular configuration of lesser apertures in said substrate and a plurality of radially inwardly directed projections aligned with at least some of said lesser apertures of said substrate and extending over said lesser apertures in cantilevered fashion; and a ground strap one end of which is fixed to said metallic plate and the other end of which is connected to ground potential, said device being mounted between said tube and said socket with said pins passing through said lesser apertures closely adjacent said inwardly directed apexes whereby a plurality of spark gaps are formed between said projections and the pins of a cathode ray tube. 